The invention relates to a program-controlled automated machines, and a method for the operation of such a machine. In particular, the invention relates to a production machine or machine tool, such as a program-controlled automation system having an industrial robot.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Production machines and machine tools, referred to herein as “machines”, for short, are known per se. A printing machine is one example of a production machine. The term “machine tool” is conventionally used in mechanical engineering and toolmaking to refer to all machines used for processing workpieces with tools, among other things, especially the so-called “NC” or “CNC” numerically-controlled machines. It is well-known that an industrial robot is a programmable universal machine that is intended and equipped for processing and handling workpieces, and/or for their assembly.
In the case of machines of the type mentioned in the introduction, real-time communication is required between the components which they incorporate, for example communication between the drive components for axis drives or the like, and network nodes that function as a layer-3 switch are also known.
The conditions that must be satisfied in the context of real-time communication are particularly strict. Usually the cycle times, that is, the reaction times, are 250 μs or 125 μs. In individual cases, cycle time as short as 31.25 μs can be provided and needed. Any infringement of the cycle/reaction time criteria referred to below as the “cycle time” for short, will inevitably result in the invalidity of the transmitted data concerned. Infringements of the cycle time must also be monitored. The usual tolerances lie at a low multiple of 100 ns.
The cycle time is relevant not only for communication, but for the entire system of the machine concerned. A machine with several axes incorporates, as the drive components, several so-called “motor modules”, each having a power component. One or several sensors is/are assigned to each motor module. In what follows, the motor modules and the sensors are referred to individually and collectively as “components”. For a machine with several axes, and correspondingly several components, the following steps must be completely worked through in succession within the cycle time:    1. Detection and processing of the measured values in the components    2. Transmission of the measured values over the network to a central unit of the machine concerned    3. On the basis of the measured values, calculation of new set-point values by means of the central unit (for example in the form of the execution (calculation) of control algorithms)    4. Transmission of the set-point values over the network from the central unit to the components    5. Processing and application of the new set-point values in the components
In what follows, reference will also be made to these steps, using their numbering, as “Step 1”, “Step 2” etc. The communication relationships which are used/which result refer not only to the individual motor modules (MM) but also to the units incorporated in the motor modules, for example sensors in the form of so-called motor measurement systems (MMS) and direct measurement systems (DMS). An implication of this—in respect of the cycle time—is that a relative number of components require correspondingly as many transmissions with comparatively small data volumes.
These requirements can only be met by a so-called time-slot method. Such a time-slot method is basically known per se. With it, in the start up of the machine concerned the exact communication requirements within the machine are determined, and each individual transmission is precisely planned with respect to a time point relative to the cycle time (time-slot). In operation, this plan is then simply processed cyclically. Each component then “knows” exactly where the previously planned time-slots lie for its own messages which are to be sent, and it always sends them exactly at the appropriate time points. This sending takes place even then when the prerequisites may not be present, for example because data items, in particular locally recorded measured values, are not yet available. The result of this “time-slot” monitoring mentioned above is that data items marked as invalid are sent.
In the time-slot method, the sending of messages presumes an exact synchronization of all the components. All the components thus work using a common time base. This is effected via synchronization messages and digital His. The tolerances for isochronicity are mostly less than 50 ns.
Although the sending of messages in the time-slot method is an established and proven technique, there are in practice certainly still some problems. Thus, a network with its components connected for communication purposes often includes areas with conditions which are mechanically or electrically more difficult. One example of such more difficult mechanical conditions is trailing cables. An example of conditions which are made electrically more difficult is strong interfering fields. In such areas, the fault-free rate of data acquisition which can be achieved is limited. In addition, in a network links are often required between areas with dangerous voltages and areas with low voltages, wherein safe physical contacts must be possible. Because of the high voltage-proof galvanic isolation which is then required, high data rates are unreasonably expensive for these links. Finally, the large number of different components normally does not permit all the components to be provided with the latest network technology. Even in facilities which are being newly configured, components with different versions of the network technology must often communicate with each other. This also often leads to different data rates in parts of the network.
Apart from this, one special requirement on communication arises in the case when power components are connected in parallel. The compensation which is then necessary for unavoidable differences in the behavior of these power components can be effected in hardware (inductances) and in software (compensation regulator). The higher the performance of such a compensation regulator, the smaller the inductances' dimensions can be. However, an additional prerequisite for high-performance compensation regulation is that the communication between the motor modules of the power components involved goes far beyond the usual level of such requirements. This results in an additional load on the communication network.